1. Field of the Invention
The present invention relates to a low permeable hose and to a method for producing it. More particularly, the present invention relates to a low permeable hose that has an increased resistance to the permeation of refrigerants, fuel gases, blowout gases and the like and to a method for producing such a hose.
2. Description of the Related Art
Conventional hoses generally employed as a hose for transporting a refrigerant for air conditioners of automobiles have a refrigerant barrier layer, made of a polyamide resin or a modified butyl rubber and arranged in an inner pipe thereof.
Also, to improve the low permeability of a refrigerant transporting hose, a technology using a metal vapor deposition film as the refrigerant barrier layer has been developed. For example, JP 02-209224 A discloses a low permeable rubber hose having a thin film made of a certain metal formed on an outer peripheral surface of a synthetic resin made inner pipe by a sputtering method or an ion plating method. Also, JP 02-209225 A discloses a low permeable rubber hose having a dry plated thin film of a metal or metal compound formed on an outer peripheral surface of a synthetic resin made inner pipe. However, although the formation of such a metal vapor deposition film improves the low permeability of the refrigerant barrier layer, another problem arises. That is, because it is very thin, the metal vapor deposition film cannot follow the contour of the rubber hose that is deformed to a greater extent upon use and pinholes and cracks occur in the metal vapor deposition film, from which the refrigerant leaks.
On the other hand, with a view to maintaining the low permeability to the refrigerant in spite of the deformation of the rubber hose, a rubber hose that uses a metal foil as a refrigerant barrier layer has been proposed. For example, JP 02-80881 A discloses a flon low permeable flexible hose using a laminate film composed of a metal foil and a plastic film as a barrier layer. However, the laminate film composed of a metal foil and a plastic film as disclosed in the above publication cannot maintain the low permeability to the refrigerant due to the breakage of the metal foil when the rubber hose is deformed. In addition, the above publication contains no specific teaching on the method of bonding the metal foil and the plastic film, which are considered to be materials difficult to bond to each other, and the method of bonding the nylon tube, i.e., inner tube of the hose, to the barrier layer.
Accordingly, a low permeable hose that can sufficiently endure deformation of the rubber hose and has excellent permeation resistance to refrigerants, etc. and a specific method for producing such a low permeable hose are keenly demanded.
An object of the present invention is to provide a low permeable hose that is excellent in refrigerant permeation resistance (barrier property to the refrigerant) and gas permeation resistance and has in the inside thereof a refrigerant barrier layer composed mainly of a metal layer that can follow the deformation of the hose.
Another object of the present invention is to provide method for producing a low permeable hose that is free of peeling off of the refrigerant barrier layer composed mainly of a metal layer from the hose upon use.
As a result of extensive studies, the present inventors have found out that use of a laminate film having resin films sandwiching therebetween a metal layer can improve the low permeability to refrigerants, various gases and so forth and maintain low permeability in case of deformation of the hose. Also, they have found out that when splicing such a laminate film to the rubber layer where the temperature of the refrigerant to be transported is low, heating the laminate film at a temperature no lower than the melting point of the resin contained in the resin layer that constitutes the surface of the laminate film and at the same time vulcanizing the rubber layer can give rise to firm splicing of the laminate film and rubber layer. On the other hand, in the case where the temperature of refrigerant is increased up to hundred and several tens degrees (xc2x0C.), provision of an adhesive layer made of a phenol resin composition can give a high adhesion strength such that if the temperature of the refrigerant is increased, the laminate film will not peel from the rubber layer. The present invention has been completed based on the above discoveries.
That is, according to a first aspect of the invention, the present invention provides a low permeable hose having at least a refrigerant barrier layer and a rubber layer, wherein the refrigerant barrier layer is a laminate film having a structure such that resin layers sandwich a metal layer therebetween and having an elongation at breakage of 10% or more, and preferably 30% or more.
Here, it is preferred that the metal layer is a metal foil and at least one of the resin layers has thereon a strength maintaining layer. Preferably the strength maintaining layer is a layer composed of a polyamide resin composition or a polyester resin composition.
Also, it is preferred that the strength maintaining layer is an innermost layer of the resin layer and the strength maintaining layer and the metal layer are bonded to each other with an aromatic polyester based adhesive.
Furthermore, it is preferred that an outermost layer of the resin layer is a polyolefin layer composed of a polyolefin resin composition. The polyolefin resin composition preferably contains a polyolefin resin having a melting point of 120xc2x0 C. or more. Also, it is preferred that the rubber layer is constituted by a rubber composition whose vulcanization temperature is 120xc2x0 C. or more.
According to a second aspect of the invention, the present invention provides a low permeable hose having at least a refrigerant barrier layer and a rubber layer, wherein the barrier layer is a laminate film having a structure such that resin layers sandwich a metal layer therebetween and having an elongation at breakage of 10% or more, and preferably 30% or more.
Here, it is preferred that the metal layer is a metal foil and at least one of the resin layers has thereon a strength maintaining layer. Preferably the strength maintaining layer is a layer composed of a polyamide resin composition or a polyester resin composition.
Also, it is preferred that the strength maintaining layer is an innermost layer of the resin layer and the strength maintaining layer and the metal layer are bonded to each other with an aromatic polyester based adhesive.
Also, it is preferred that an outermost layer of the resin layer is an adhesive layer composed of a pherol resin based composition.
According to a third aspect of the invention, the present invention provides a method for producing a low permeable hose having at least a refrigerant barrier layer and a rubber layer, comprising superimposing the refrigerant barrier layer and the rubber layer, wherein the refrigerant barrier layer is a laminate film having a structure such that resin layers sandwich a metal layer therebetween and having an elongation at breakage of 10% or more, and preferably 30% or more; and
wherein the method comprises the steps of:
laminating the resin layers in the refrigerant barrier layer and the rubber layer; and
heating the refrigerant barrier layer and the rubber layer to a temperature no lower than a melting point of a resin that constitutes the resin layers to melt the resin and vulcanizing the rubber layer, thereby splicing the refrigerant barrier layer and the rubber layer.
Here, it is preferred that the resin layers in the refrigerant barrier layer have a polyolefin layer composed of a polyolefin resin composition. Also, it is preferred that the refrigerant barrier layer and the rubber layer are spliced by heating them at 120xc2x0 C. or more. Furthermore, it is preferred that in the refrigerant barrier layer, at least one splicing surface between the metal layer and the resin layers is coated with an aromatic polyester based adhesive before the lamination.
In a fourth embodiment, the present invention provides a method for producing a low permeable hose having at least a refrigerant barrier layer and a rubber layer, comprising superimposing the refrigerant barrier layer and the rubber layer,
wherein the refrigerant barrier layer is a laminate film having a structure such that resin layers sandwich a metal layer therebetween and having an elongation at breakage of 10% or more, and preferably 30% or more,
wherein the refrigerant barrier layer is a laminate film whose resin layer that constitutes a surface thereof has an adhesive layer composed of a phenol resin based composition, and
wherein the method comprises the step of laminating the adhesive layer and the rubber layer, thereby splicing the refrigerant barrier layer and the rubber layer.
Here, it is preferred that in the refrigerant barrier layer, at least one splicing surface between the metal layer and the resin layers is coated with an aromatic polyester based adhesive before the lamination.
The low permeable hose of the present invention is excellent in refrigerant permeation resistance so that it can be advantageously used as a hose for transporting various refrigerants, in particular refrigerants for air conditioners of automobiles. Also, according to the method for producing a low permeable hose of the present invention, a low permeable hose that is excellent in splicing property between the rubber layer and the refrigerant barrier layer as well as in refrigerant permeation resistance can be obtained.